DE1551454A1 - Liquid metal cooling system - Google Patents

Description

Patent attorney DipUng. Richard iiiiiler-borner

Complete Üaos-Heinridi Way : BMlie-Dahlem, Podbielskiallee 68

17 981/2 Berlin, June 16, 1967

EUROPEAN ATOMIC COMMUNITY (EURATOBT)

Patent application

Liquid metal cooling system

The invention relates to a liquid metal cooling system for heated walls, especially for nuclear reactors

Liquid metals, especially alkali metals, have lately been found Offered as a good coolant for fast nuclear reactors because of its radiation resistance, high boiling point and time the low moderator effect. On the other side iot the boil Still difficult to control because of the delay in boiling Water can take on significant values and, moreover, the boil · » Due to the high thermal conductivity, use is explosive and at the same time

0098U / 0769

- 2 χ EUH / C / 282V67 - 1136 d

takes place throughout the metal volume. Also with artificial boiling germs This problem has not been completely solved on structured surfaces etc. On the one hand, the boiling must be for safety reasons can be avoided in nuclear reactors as long as the boiling process is not yet dynamically controlled, on the other hand a cooling cycle with a liquid-vapor-liquid phase change can dissipate much larger amounts of heat than a monophaser Cycle.

There is a possibility of liquid metal cooling with phase change recently in the so-called heat pipes; these are tubes that are closed on all sides and are almost completely filled with metal vapor, which condenses on one end of the tube in a heat sink, whereupon the condensate in longitudinal capillaries on the inner wall of the tube flows back to the heat source at the other end. However, since Heat pipes have to do without pumps (the liquid transport is based solely on capillary forces!) the heat transport is even lower here than with a normal cooling channel without evaporation.

It is the object of the invention to provide an effective cooling system for heated walls indicate the liquid metal in e ^ .ner cooling cycle used with phase change without boiling problems occurring.

The invention consists in that a finely porous layer is placed in front of the walls at a small, defined distance and that the liquid metal is underneath in the gap given by the distance

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such a pressure that it is at the heating temperature does not yet boil, while when it passes through the pores of the wall it reaches an area of lower pressure, so that it evaporates and then flows to a heat sink, e.g. a heat exchanger. Advantageously, the pressure in the gap is through a Liquid metal container generated, which is arranged at a suitable height above the wall.

The invention is described below on the basis of an exemplary embodiment explained in more detail with the help of rtroici figures:

1 shows a partial section through a heating rod

Cooling system according to the invention;

Fig. 2 is a diagram showing the temperature and pressure distribution in the radial direction according to FIG.

3 shows a section through an entire nuclear reactor

in scheraatic representation with the invention proper cooling system.

The principle on which the invention is based is best explained with reference to FIG. 1, in which an internally heated rod 1 can be seen which is surrounded by a porous tube 2. The rod diameter and the inside diameter of the pipe are chosen so that an even, defined distance (gap 3) remains between the two. Liquid coolant, e.g. a Alkali metal pressed in under pressure.

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The gap width is optimized in the order of magnitude of up to 1 mm so that the required coolant length can be specified without excessive pressure losses. Too wide a gap, on the other hand, would impair the TJänno transmission. The pressure on the refrigerant is co gov £ _f hlt that boiling will be suppressed at a maximum hot rod. In general, a pressure difference between the gap and the steaming space outside the porous tube of 0.5 atm is sufficient.

Under the action of this pressure difference, a certain amount of coolant per unit area is pressed through the tube 2 and evaporates as soon as it emerges from the pores. It can be seen that this cooling process only works reliably when using metals with their high thermal conductivity. In Fig. 2 the temperature loss is drawn in the radial direction from the rod surface on. The temperature (solid line) drops only slightly in the gap and in the pipe, so that the evaporation when exiting the pores is ensured solely by the pressure difference (dashed line). (The pressure jump when exiting the pores is incidentally caused by the high surface tension of the liquid metal and the meniscus formation in a capillary channel).

Experiments have shown that pore clogging Can be avoided, as evaporation is only in the pore openings takes place. Impurities that settle there when they evaporate are replaced by the hot liquid metal flowing in replaced automatically for some time. A cleaning cycle needs

0098U / 0769 _BAD original

• So only to be passed over the reactor floor to avoid all foreign bodies to remove.

The size and density of the pores in the pipe is chosen so that such an amount of liquid at the selected liquid pressure passes through the pores that just complete evaporation is guaranteed. Both the licking of the liquid on the steam " side as well as the drying out of the pores is to be prevented. This condition appears difficult when the heating output changes, however, it is actually easy to maintain because of the pumping action of the capillary forces. Namely, dries the outer surface of the If the pipe comes out slightly, a curved surface is created in each pore, which increases the capillary pumping effect and more Liquid metal is promoted. Calculations have shown that a change in the heating surface load in a ratio of 1:50 neither to the Licking still leads to dehydration. This allows energy densities of

W W

E.g. 500 - -ζ and 10 -5- safely separated from the same cooling arrangement

cm cm
be directed. The cooling system is therefore characterized by great stability, which is of great advantage when used in reactors for safety reasons.

In the concluding FIG. 3 , a reactor core is therefore shown in a schematically simplified form, the rod-shaped fuel elements k _{t of which,} as shown in FIG. 1, are inserted in porous tubes 5 made of sintered steel, for example. Bin reservoir 6 for the liquid metal is located above the reactor core and is connected to the columns of all fuel elements * The pressure is generated by a pump, BADOR ₁ G ₁ NAL """"""'

a constant level of the liquid metal in this reserve dr guaranteed. As shown, the pump can be located under the fuel elements via a feed line 7 Pressurize Purapraum 8.

In addition to maintaining pressure, the reservoir also fulfills the task of one very effective biological shield up; also guaranteed k there is reliable cooling of the reactor even some time after the pump fails.

The on passage of Flüssignietalls through the porous ^T? Ände resulting vapor flows in the direction perpendicular to the axis of the reactor out of the core to heat exchangers 9 to where it condenses and then passes back as a liquid over said pump back into the pump chamber. 8 The heat exchangers are arranged directly around the core edge so that the steam can flow out between the tubes 5 in all directions. The steam speed can assume the speed of sound, Ss is an adiabatic expansion with a large pressure difference.

Because of the high transport capacity due to the system according to the invention for / poor energy and the relatively small amount of coolant In essence, a compact high-speed neutron reactor with a high breeding rate can be designed in this way. But also in thermal The system according to the invention should be advantageously applicable to reactors "

0098U / 0769

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Claims (2)

Pat ent calls it "j liquid metal cooling system for heated walls" for nuclear reactors, characterized in that the walls at a small "defined distance from a fine-porous layer is upstream and that in the given through the clearance gap, the liquid metal wirdl pressed such pressure to · ₅ that in the Heating temperature * does not yet boil _B while when it passes through the pores of the wall it reaches an area of lower pressure, which evaporates and then flows to a heat sink, eg a heat exchanger. 2. Liquid metal cooling system according to claim l _t, characterized in that the pressure in the gap is generated by a liquid metal container which is arranged at a suitable height above the wall. EUR / C / 282V67 - ^B * ^D ORIGINAL 0 0 9 5 14/0769 -8-blank page